1. Field of the Invention
The present invention relates to motion detection systems and, more particularly, passive infrared motion detectors that have an adjustable field of view to facilitate their mounting in either a corner or on a wall.
2. Description of the Related Art
Passive infrared (PIR) motion detectors are well known in the art and are used to detect the presence of a human intruder by sensing the thermal energy radiated by the intruder. Generally, such PIR detectors are designed to have a horizontal field of view that has an angular range of between 85 and 90 degrees. Using this range for the field of view allows the detector to be mounted in an interior corner. By utilizing a horizontal field of view that is slightly less than 90 degrees, false alarms caused by objects on the adjacent walls can be reduced.
Oftentimes, it is desirable to mount detectors on planar walls rather than interior corners. Unfortunately, the corner-adapted detectors have a horizontal field of view of only 90 degrees. As a result, when mounted on planar walls, such detectors fail to provide coverage in the areas to the side of the detector. Accordingly, detectors having a 180 degree field of view have been proposed. Although effective for wall mounting, these detectors are not effective in interior corner mount situations. The 180 degree field intersects the walls forming the interior corner and, therefore, detects changes in thermal energy of objects on the walls. Objects on the wall, such as windows, curtains and blinds, often experience a significant change in thermal energy as the sun heats these objects. Such changes in thermal energy can be detected by the 180 degree, corner-mounted detector creating false alarms. Consequently, a need remains for an improved detector that may be effectively used in either corner and wall mounting applications and which includes a means for properly adjusting the field of view of the detector and inhibiting the incorrect installation of the detector.